Circuit for performing external pacing and biphasic defibrillation

Abstract

An external defibrillator/pacer ( 8 ) includes an output circuit ( 14 ) with four legs arrayed to form an H-bridge coupled to an energy storage capacitor. The energy storage capacitor delivers an external defibrillation pulse with stored energy during a defibrillation mode and an external pacing pulse during a pacing mode. Each leg of the output circuit contains a switch (SW 1 -SW 4 ). In a defibrillation mode, pairs of switches in the H-bridge are selectively switched to generate a biphasic defibrillation pulse. Three switches (SW 1 , SW 3 , SW 4 ) are silicon controlled rectifiers (SCRs). Gate drive circuits ( 51, 53, 54 ) are coupled to the SCRs to bias the SCRs with a voltage that allows the SCRs in response to control signals. One switch (SW 2 ) includes an insulated gate bipolar transistor (IGBT). A gate drive circuit ( 52 ) is coupled to the gate of the IGBTs to provide a slow turn-on and a fast turn-off of the IGBT. In a pacing mode, a bypass circuit or current source circuit is used to provide a current path bypassing an SCR switch (SW 3 ), which cannot be triggered by the relatively low current of pacing pulses. One of the SCRs (SW 4 ) may be replaced with an IGBT to allow generation of the pacing pulse with opposite polarity of the first phase of the defibrillation pulse.

We claim:  
     
       1. A circuit that generates a defibrillation pulse in a defibrillation mode and a pacing pulse in a pacing mode, the circuit comprising: 
       an energy storage capacitor having a first electrode and a second electrode;  
       a charging circuit coupled to the energy storage capacitor, wherein the charging circuit is configured to charge the energy storage capacitor;  
       an energy transfer circuit coupled to the energy storage capacitor, the energy transfer circuit having a first output lead and a second output lead, wherein the energy transfer circuit is configured to selectively electrically couple the first and second electrodes of the energy storage capacitor to the first and second output leads; and  
       a control circuit coupled to the charging circuit and the energy transfer circuit, wherein the control circuit is configured to cause the charging circuit to charge the energy storage capacitor to a predetermined level and, when the energy storage capacitor is charged, to control the energy transfer circuit to couple the first and second electrodes of the energy storage capacitor to the first and second output leads of the energy transfer circuit so that the energy transfer circuit provides:  
       during the defibrillation mode, an external defibrillation pulse at the first and second output leads using energy stored in the energy storage capacitor, and  
       during the pacing mode, an external pacing pulse at the first and second output leads using energy stored in the energy storage capacitor.  
     
     
       2. The circuit of claim  1  wherein the energy transfer circuit comprises four legs, a first leg of the energy transfer circuit including a first IGBT switch circuit and a second, a third and fourth leg of the energy transfer circuit each including an SCR switch circuit. 
     
     
       3. The circuit of claim  2  wherein the energy transfer circuit comprises a bypass circuit, the bypass circuit being coupled in parallel with the third leg of the energy transfer circuit, and wherein the bypass circuit is configured to provide a conductive path that bypasses the third leg of the energy transfer circuit during the pacing mode and is configured to open circuit the conductive path during the defibrillation mode. 
     
     
       4. The circuit of claim  3  wherein the defibrillation pulse is selectably provided as a biphasic pulse and the pacing pulse is provided as a monophasic pulse. 
     
     
       5. The circuit of claim  3  wherein, during the pacing mode, the control circuit is configured to determine the predetermined level in charging the energy storage capacitor to achieve a predetermined current level for a subsequently provided pacing pulse. 
     
     
       6. The circuit of claim  2  wherein the H-bride circuit comprises a current source circuit, the current source circuit being coupled in parallel with the third leg of the energy transfer circuit, and wherein the current source circuit is configured to provide a configurable current to the first output lead during the pacing mode and is configured to provide essentially no current to the first output lead during the defibrillation mode. 
     
     
       7. The circuit of claim  6  wherein, during the pacing mode, the control circuit is configured to cause the current source circuit to provide the configurable current with a predetermined current level. 
     
     
       8. The circuit of claim  6  wherein the current source circuit comprises an IGBT and a resistor. 
     
     
       9. The circuit of claim  1  wherein the energy transfer circuit comprises four legs, a first leg and a second leg of the energy transfer circuit each including an IGBT switch circuit, and a third leg and a fourth leg of the energy transfer circuit each including an SCR switch circuit. 
     
     
       10. The circuit of claim  9  wherein the H-bride circuit comprises a bypass circuit, the bypass circuit being coupled in parallel with the third leg of the energy transfer circuit, and wherein the bypass circuit is configured to provide a conductive path that bypasses the third leg of the energy transfer circuit during the pacing mode and is configured to open circuit the conductive path during the defibrillation mode. 
     
     
       11. The circuit of claim  10  wherein the defibrillation pulse is selectably provided as a biphasic pulse having a first phase with a first polarity and a second phase of a second polarity, and wherein the pacing pulse is provided as a monophasic pulse with the second polarity. 
     
     
       12. The circuit of claim  11  wherein, during the pacing mode, the control circuit is configured to determine the predetermined level in charging the energy storage capacitor to achieve a predetermined current level for a subsequently provided pacing pulse. 
     
     
       13. The circuit of claim  9  wherein the H-bride circuit comprises a current source circuit, the current source circuit being coupled in parallel with the third leg of the energy transfer circuit, and wherein the current source circuit is configured to provide a configurable current to the first output lead during the pacing mode and is configured to provide essentially no current to the first output lead during the defibrillation mode. 
     
     
       14. The circuit of claim  13  wherein, during the pacing mode, the control circuit is configured to cause the current source circuit to provide the configurable current with a predetermined current level. 
     
     
       15. The circuit of claim  13  wherein the current source circuit comprises an IGBT and a resistor. 
     
     
       16. The circuit of claim  13  wherein the current sense circuit comprises an amplifier, a transformer and a resistor. 
     
     
       17. The circuit of claim  1  wherein the energy transfer circuit comprises four legs, each of the four legs of the energy transfer circuit including an IGBT switch circuit. 
     
     
       18. The circuit of claim  17  wherein the defibrillation and pacing pulses are selectably provided as a biphasic pulse or monophasic pulse. 
     
     
       19. The circuit of claim  18  wherein the defibrillation pulse is a biphasic pulse having a first phase with a first polarity and a second phase of a second polarity, and wherein the pacing pulse is a monophasic pulse with the second polarity. 
     
     
       20. The circuit of claim  18  wherein the defibrillation pulse is a biphasic pulse having a first phase with a first polarity and a second phase of a second polarity and the pacing pulse is a biphasic pulse having a first phase of the second polarity and a second phase of the first polarity. 
     
     
       21. The circuit of claim  17  wherein, during the pacing mode, the control circuit is configured to determine the predetermined level in charging the energy storage capacitor to achieve a predetermined current level for a subsequently provided pacing pulse. 
     
     
       22. The circuit of claim  17  wherein the H-bride circuit comprises a current sense circuit coupled to the energy storage capacitor and the control circuit, and wherein the current sense circuit is configured to detect a current level of current provided by the energy storage capacitor when the circuit is providing a pacing pulse. 
     
     
       23. The circuit of claim  22  wherein, during the pacing mode, the control circuit is configured to cause the third and fourth legs of the energy transfer circuit to conduct a predetermined level of current when the circuit is providing a pacing pulse. 
     
     
       24. The circuit of claim  1 , wherein the energy transfer circuit is configured as an H-bridge. 
     
     
       25. The circuit of claim  1 , wherein the energy storage capacitor is a single capacitor. 
     
     
       26. A method of externally providing a defibrillation pulse or a pacing pulse to a patient from a single unit, the method comprising: 
       charging an energy storage capacitor;  
       during a defibrillation mode, transferring energy from the energy storage capacitor to the patient in a defibrillation pulse; and  
       during a pacing mode, transferring energy from the energy storage capacitor to the patient in a pacing pulse.  
     
     
       27. The method of claim  26  wherein an energy transfer circuit is used to transfer energy from the energy storage capacitor to the patient in both the defibrillation and pacing modes. 
     
     
       28. The method of claim  26  wherein the energy storage capacitor is charged to a predetermined level so that the pacing pulse has a current of a predetermined level. 
     
     
       29. The method of claim  26  wherein the pacing pulse is a biphasic pulse. 
     
     
       30. An apparatus for providing to a patient a defibrillation pulse during a defibrillation mode and a pacing pulse during a pacing mode, the apparatus comprising: 
       an energy storage capacitor;  
       charging means for charging the energy storage capacitor;  
       switch means coupled to the energy storage capacitor for selectively transferring energy from the energy storage capacitor to the patient externally; and  
       control means for causing the switch means to transfer energy from the energy storage capacitor to the patient externally in a defibrillation pulse during the defibrillation mode, and for transferring energy from the energy storage capacitor to the patient externally in a pacing pulse during the pacing mode.  
     
     
       31. The apparatus of claim  30  wherein the switch means comprises an energy transfer circuit, wherein the energy transfer circuit is selectively configurable to transfer energy from the energy storage capacitor to the patient in both the defibrillation and pacing modes. 
     
     
       32. The apparatus of claim  30  wherein the control means is configured to cause the charging means to charge the energy storage capacitor to a predetermined level wherein the pacing pulse has a current of a predetermined level. 
     
     
       33. The apparatus of claim  30  wherein the pacing pulse is a biphasic pulse.